Genotype-environment interaction is pervasive in forest genetics. Delineation of spatial breeding zones (BZs) is fundamental for accommodating genotype-environment interaction. Here we developed a BZ classification pipeline for the forest tree Eucalyptus globulus in 2 Australian regions based on phenotypic, genomic, and pedigree data, as well on a detailed environmental characterization (“envirotyping”) and spatial mapping of BZs. First, the factor analytic method was used to model additive genetic variance and site–site genetic correlations (r_B) in stem volume across 48 trials of 126,467 full-sib progeny from 2 separate breeding programs. Thirty-three trials were envirotyped using 145 environmental variables (EVs), involving soil and landscape (71), climate (73), and management (1) EVs. Next, sparse partial least squares-discriminant analysis was used to identify EVs that were required to predict classification of sites into 5 non-exclusive BZ classes based on r_B. Finally, these BZs were spatially mapped across the West Australian and “Green Triangle” commercial estates by enviromic prediction using EVs for 80 locations and 15 sets of observed climate data to represent temporal variation. The factor analytic model explained 85.9% of estimated additive variance. Our environmental classification system produced within-zone mean r_B between 0.76 and 0.84, which improves upon the existing values of 0.62 for Western Australia and 0.67 for Green Triangle as regional BZs. The delineation of 5 BZ classes provides a powerful framework for increasing genetic gain by matching genotypes to current and predicted future environments.

The expansion of red mahogany (Eucalyptus pellita) plantations in the wet tropics of northern Australia has increased interest in the domestication of the species. A review of an overseas breeding population was undertaken to enhance our current understanding of genetic parameters for E. pellita, which are essential for the development of advanced-generation breeding programs. The large genetic differences between and within provenances, as well as the moderate heritability estimates for growth and form traits, imply that tree breeding can create improved breeds and reduce variability in plantation forests. Our analysis suggests that breeding value predictions of parents tested in first-generation provenance—progeny trials are less indicative of an individual's genetic merit than breeding values generated from second-generation trials. The low heritability estimate in the first generation relative to the second generation and the reduced inter-generational correlations will influence the level of genetic gain that can be realised. The implications of these findings for the management of E. pellita breeding populations and the production of improved seed for plantation forestry in the tropics are discussed.